Only a limited number of molecules with demonstrated therapeutic value can be transported through the skin via unassisted or passive transdermal drug delivery. The main barrier to transport of molecules through the skin is the stratum corneum (i.e., the outermost layer of the skin).
Devices including arrays of relatively small structures, sometimes referred to as microneedles or micro-pins, have been disclosed for use in connection with the delivery of therapeutic agents and other substances through the skin and other surfaces. The devices are typically pressed against the skin in order to pierce the stratum corneum such that the therapeutic agents and other substances can pass through that layer and into the tissues below.
A number of processes have been proposed for preparing microneedles and microneedle arrays. These processes include direct methods, that is, methods where a microneedle or microneedle array is directly fabricated, such as use of photolithography to prepare silicon microneedles. These processes also include indirect methods, that is, methods where a replication tool (e.g., a mold) is first prepared having the negative image of a microneedle or microneedle array and a microneedle or microneedle array is molded against the replication tool. However, microneedles are very fine structures that can be difficult to prepare in a precise and cost-effective manner.